1. Field of the Invention
The present invention relates to a thermal printer, a thermal printing method and a conveyor for recording material. More particularly, the present invention relates to a thermal printer which can be easily combined with a personal computer, a video player or the like, and a thermal printing method and a conveyor for recording material used with the thermal printer.
2. Description Related to the Prior Art
A tower type of personal computer has been recently used widely. The personal computer of this type has a feature of high extensibility, and includes a plurality of so-called bays, or spaces for setting respective relevant devices such as a flexible disk (FD) drive device, a hard disk device, a compact disk (CD) drive device and an MO drive device. Each bay can contain such a peripheral unit which is approximately 146 mm wide, 41 mm high, and 220 mm deep.
There is another suggestion of the personal computer in which a scanner is set in the bay with intention of extension, the scanner previously having been connected externally to a computer in a conventional manner. With the scanner or other peripheral units incorporated in the body of the personal computer, convenience and ease in use of them is increased. There is no need of externally connecting operation. Furthermore peripheral units to be installed do not require installing spaces in a room, although such are still required by external peripheral units.
It is conceived to combine a color printer with the personal computer of the tower type as one of the peripheral units, because the color printer will be usable with high frequency and much convenience. However there is no color printer which could be mounted in the bay of the personal computer, because the color printer in the prior art is too large and cannot be constructed in a small size suitable to the bay.
There is a color thermal printer of a sublimation type or wax transfer type, which is used with ink ribbon. The ink ribbon is wound in a roll form, which inevitably has a size of 25-30 mm at the minimum. It is impossible to construct the printer with a thickness equal to or less than 41 mm. Moreover the ink ribbon, when used up, must be renewed. If the bay contained the color thermal printer of this type, the entirety of the printer must be pulled out and opened for the purpose of renewal of the ink ribbon.
There is no ink jet printer which would be mounted in the bay of the personal computer, because sizes of an ink tank and a recording head of an ink jet printer cannot be reduced and are inconsistent to the smallness of the bay. The ink jet printer has a mechanical system of a serial printer, and also requires a mechanism for moving the recording head. Also the ink jet printer must be supplied with ink periodically. A body of the ink jet printer must be drawn and opened before the ink can be supplied. Both the head moving mechanism and supply of ink cause problems in failure of obtaining compactness of the body.
Among various types of color printers, there is a color thermal printer in which color thermosensitive recording material of direct thermal recording is heated to develop color by itself. The color thermal printer does not use ink ribbon, ink or other expendable material, and does not need to be open for the purpose of supplying anything expendable. Therefore this type of the color thermal printer has suitability to being contained in the bay of the personal computer.
The recording material includes a support, and a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer, all of which are overlaid on the support. Among the three layers, the yellow coloring layer, which lies the farthest from the support, has the highest heat sensitivity. In the color thermal printer, a thermal head is pressed against the recording material, to print a yellow image to the yellow coloring layer line by line at first. Then a yellow fixer applies ultraviolet rays to the yellow coloring layer to fix the yellow image. The thermal head prints a magenta image to the magenta coloring layer next. A magenta fixer applies ultraviolet rays to the magenta coloring layer to fix the magenta image. Finally the thermal head prints a cyan image to the cyan coloring layer, so as to obtain a full-color image.
The thermal recording and the fixation are effected while the recording material is conveyed in a manner relative to the thermal head and the fixer unit. An example of various structures for conveying the recording material is a back-and-forth moving structure. The color thermal printer with this structure includes a recording material conveyor device or a conveyor roller set, which is constituted by a capstan roller and a pinch roller. The capstan roller is driven by a motor to rotate. The pinch roller has a diameter smaller than that of the capstan roller. The conveyor roller set nips the recording material and conveys it back and forth, while the thermal head pressurizes and heats the recording material to develop the three colors sequentially, that are yellow, magenta and cyan.
However there is no known color thermal printer which would be mounted in the bay of the personal computer, because of considerable largeness of parts and components in a color thermal printer and a large space required for their arrangement. For the three coloring layers, temperature at which each coloring layer starts being colored is different. Therefore the color thermal printer of the direct recording type inevitably has the maximum heating temperature higher than that of a wax transfer type of thermal printer, in which the temperature at which each coloring layer starts being colored is equal between the coloring layers. In the direct recording type, generated heat is considerably much due to the heating temperature. The problem of considerable generated heat should be solved in mounting the color thermal printer in the bay of the personal computer, in addition to the dimensional problems of the color thermal printer and its parts.